1. Field of the Invention
The present invention relates to a method of manufacturing hollow bodies in a multi-cavity blow molding machine having an extrusion station, a calibration station spaced from the extrusion station and located parallel thereto, and a blow mold, with the method including inserting, into spaced mold halves of the blow mold, plastic hose-shaped blanks at the extrusion station and closing the blow mold, displacing the closed blow mold from the extrusion station to the calibration station, inserting, at the calibration station, blow mandrels into respective cavities of the closed blow mold, lifting, after expiration of a predetermined blow time, the blow mandrels, together with the blown hollow bodies to an intermediate position and removing the blown hollow bodies from the blow mandrels, thereafter, lifting the blow mandrels to their initial position, and displacing the blow mold from the calibration station back to the extrusion station.
The present invention also relates to a blow molding machine for effecting the method.
2. Description of the Prior Art
The above-described multi-cavity or long-stroke blow molding machines are disclosed, e.g., in European Patent No. 0 570 393 B1and prospect "Long-Stroke Blow Molding Machines" of the firm "Fischer-W. Muller Blasformetchnik Gmbh", January 1996, an assignee herein. In these blow molding machines, the extrusion and the blow (calibration) stations are arranged along a vertical elongate central plane under each other on a line along which the blow mold reciprocates. The time of a cycle of a blow-molding machine depends not only on the blow time but also, to a great extent, on the down time associated with the displacement of the blow mold and closing and opening of the mold halves. The linear displacement stroke in these blow molding machines increases with each additional cavity in the blow mold. This is because the length of the blow mold, together with the closing system, in the direction of the connection line, should exceed the width of the blow mold, which results in a proportional increase of the displacement stroke with additional cavities, resulting in increase of the displacement time. With short blow or cooling down time, which amounts to about 5 sec. for a typical surface of a hollow body produced with these blow molding machines, the displacement time can be of the same order as the blow and cooling down time when the blow mold has more than four cavities. With the blow mold having more than four cavities, the displacement path can reach, e.g., 1600 mm, with the process speed being also influenced by a high weight of the closing system, which can amount to several ton. E.g., the weight of the closing system can be above 6 ton. Such a large mass cannot be displaced from one position into another sufficiently rapidly, without using a very powerful drive and associated with it excessive costs. It may happen that down time is greater than the blow and cooling down time, which adversely affects the economical use of a long-stroke blow molding machine, as with the increase of the down time, the output of a blow molding machine decreases.
Accordingly, an object of the present invention is to provide a method of and a multi-cavity blow molding machine for manufacturing hollow bodies with which the cycle time and, in particular the time associated with the displacement of the mold between the extrusion and calibration stations is reduced to a minimum.